1. Field of the Invention
The present invention relates generally to structures and materials used in the formation of orthopedic casts. The present invention relates more specifically to a layered, open cell, fabric material impregnated with a curable polymer or pre-polymer resin that may be shaped and formed prior to curing into a rigid cast.
2. Description of the Related Art
Orthopedic casting materials have evolved over time from the earlier plaster of Paris and cotton gauze based casts to the more recent synthetic orthopedic casting tapes. Plaster of Paris based casts suffered from many difficulties that included being generally air impermeable, being subject to deterioration in contact with water, and being very heavy and bulky. The basic structure of the more recent synthetic casts involves a fabric sheet or tape, usually of fiberglass, that is impregnated with a liquid resin that cures and hardens in air over a short period of time. Alternate materials include thermoplastic resins that are formable at a temperature higher than room temperature but not so high as to be uncomfortable to the patient or the individual putting the cast material in place. In either case the result is a strong, relatively lightweight cast that, after curing, is not subject to deterioration in contact with water.
Fiberglass/Polymer Resin based cast materials typically come in two structural forms. The basic form involves a roll of tape anywhere from one to five inches wide that is applied by wrapping the tape around the limb to be cast. A second general structural form involves a pre-cut sheet of the material sized and shaped to fit around a specific appendage such as a wrist and forearm or an ankle and foot. The latter configuration is typically easier to apply but less conformable to the variety of sizes and shapes of limbs. The former structure (tape) is more versatile but is generally more difficult to apply.
The optimal characteristics of casting materials can be countervailing or conflicting in many cases. Obviously the material must result in a cast of sufficient strength to protect the healing limb. There is also however the desire for the cast to be lightweight and less bulky. As indicated above, it is desirable for the casting material to be readily formable prior to curing so as to more closely support and guard the limb. The resin-based materials should not overly adhere to the patient's skin or to the hands or gloves of the individual putting the cast in place. It is also important for the material to be readily removable when the limb has healed. Finally the finished cast should be resistant to deterioration in contact with water (and perspiration and the like) but should also be breathable. Significant skin maceration and patient discomfort can occur as a consequence of deficiencies in breathability. It has been most difficult to provide a material that is sufficiently strong and at the same time is lightweight and breathable.
There have been many efforts to improve upon both the structures and substance of the basic fiberglass/polymer resin casting material. Some of these efforts have focused on the type of resin used and the benefits of specific compositions. Other efforts have focused on the structure of the foundation fabric and the benefits of specific weaves and fiber geometry. Various patents reflecting some of these efforts include the following:
U.S. Pat. No. 5,584,800 issued to Scholz et al. on Dec. 17, 1996 entitled METHOD OF ENCLOSING A BODY MEMBER USING AN APERTURED EXTRUDED SHEET describes an extruded casting sheet made of a low temperature thermoplastic polymer that is soft and pliable above about 90° C. The material described may also include filler associated with the resin to improve its handling characteristics.
U.S. Pat. No. 5,461,885 issued to Yokoyama et al. on Oct. 31, 1995 entitled SUBSTRATE FOR RETAINING A HARDENABLE COMPOSITION describes specific fabric knit structures that are impregnatable with hardenable resin by capillary action. The material described is directed to combining strength and good air permeability.
U.S. Pat. No. 4,856,502 issued to Ersfeld et al. on Aug. 15, 1989 entitled CURABLE RESIN COATED SHEETS HAVING REDUCED TACK describes a non-woven fiber material that leaves small apertures or openings in the fabric sheets. The focus of the patent, however, is on the incorporation of additive or bound lubricants in the resin to facilitate the application of the cast without undesirable adhesion.
U.S. Pat. No. 4,841,958 issued to Ersfeld et al. on Jun. 27, 1989 entitled NONWOVEN ORTHOPEDIC CASTING MATERIALS WITH APERTURES describes yet another foundation made of a non-woven stretchable fabric impregnated with a curable prepolymer resin. The fabric is made of fiber bundles that receive and retain the resin and which form small openings between the bundles that remain open after curing.
U.S. Pat. No. 4,683,877 issued to Ersfeld et al. on Aug. 4, 1987 entitled ORTHOPEDIC CASTING ARTICLE AND METHOD describes a pre-cut, shaped “blank” of layered cast material that includes an extensible woven fabric and a layer of extensible foam. The pre-cut casting blank is sized and shaped to fit a particular limb and is initially held in place (prior to curing) by a number of clips that secure an edge of the material to the surface of the material upon wrapping around the limb.
U.S. Pat. No. 3,998,219 issued to Mercer et al. on Dec. 21, 1976 entitled ORTHOPEDIC SPLINT AND METHOD FOR FORMING SAME describes a multi-layered cast material comprising a central cellular core and inner and outer layers that sandwich the core and which when cured are rigid and supportive. Optional layers of foam material may be placed between the core and the inner and outer layers to provide better interlock between the layers (to reduce shifting between the layers).
Although a number of the materials described in the above references have as their stated goal a certain amount of air permeability, such properties remain less than optimal given the small size (on the order of 1 mm or less) of the apertures formed. In addition, none of the above materials accomplish much in the way of significantly reducing the size and weight of the finished cast. In general it is the resin (in a cured state) that provides the structural strength to the cast it is also the resin that contributes the most to the weight of the cast. Because of this problem, prior efforts have greatly limited the size of the openings or apertures in the fabric in order to maintain a sufficient amount of hardenable resin dispersed throughout the cast tape or sheet.